The invention relates to field effect transistors of the type wherein the conductivity of a channel in a semiconductor body is affected by a charge on a gate positioned adjacent to that channel and to the improvement in circuit performance thereof through employing a high temperature superconductor material in the gate.
In the technology involving field effect transistors, as packing density and performance demands increase, the detracting effects of resistance and capacitance parasitics are being found to be serious in the type of field effect transistor (FET) having a metal or polysilicon gate. At the smallest dimensions, a quarter micron and smaller, the gate resistance becomes a serious detractor due to the RC time constant of the gate. In the metal-silicide gate FET, at small dimensions, the work function of typical metals limits performance. The choice of materials that can be employed in the gate is limited by requirements forced by the work function and compatibility with the processing techniques used in very large scale integrated circuits. It is also known that there are advantages in lower temperature of the order of 77xc2x0 K. operation and, in fact, it is accepted that there is about a 30% performance increase in the devices themselves. Further, with low temperatures, lower noise margins are encountered and lower voltages may be used.
The use of an oxide or ceramic superconductor material that is in the superconducting state in the gate of semiconductor channel FET provides improved performances through practical elimination of the RC time constant of the gate and the providing of a work function that allows convenient threshold control. In depletion mode FET devices, the proper work function permits operation at 77xc2x0 K. Oxide or ceramic superconductor materials are compatible with standard integrated circuit processing techniques and temperatures.